Who best helps his chances against Democratic President Barack Obama in the Nov. 6 election? Does he pick someone who can help him win a state, or a Latino to reach out to Hispanics? A woman?

Romney advisers are adamant about the most significant requirement of the job, that the person selected have the ability to immediately step into the presidency if needed.

"I honestly believe he wants someone who can be president. Governing comes first and the politics comes second," said a senior Romney adviser.

Charlie Black, an informal Romney adviser and veteran Republican strategist, said that beyond being able to serve, a second requirement is needed. "Politically you want to have someone who does no harm," he said.

In 2008, Republican hopeful John McCain made a splash by choosing relative unknown Sarah Palin as his vice presidential nominee. But the former Alaska governor ended up being seen as a liability, committing gaffes and failing to grasp policy issues.

President George H. W. Bush's choice of Indiana Senator Dan Quayle was ridiculed after the pair took office and his vice president earned notoriety for gaffes and errors.

The name most associated with Romney in the last week is Ryan who looked to have a personal chemistry with the former Massachusetts governor when they campaigned in Wisconsin.

The two men appeared jointly before crowds, casually let each other answer voters' questions and stood side by side as they handed out sandwiches at a fast food restaurant. Romney aides noted the two men developed a good rapport.

Ryan is the 42-year-old chairman of the House of Representatives Budget Committee and author of a budget plan loved by conservatives and hated by Democrats.

His presence on the ticket could help Republican chances of winning Wisconsin for the first time since 1984, and he could rally conservatives who are unenthusiastic about the former Massachusetts governor.

But Ryan's presence could also draw more scrutiny of his plan for budget cuts.

CONSERVATIVE CHOICES

Rubio offers a solid conservative message plus, as a Cuban-American, he could help swing Hispanic voters in the traditional battleground state of Florida.

Portman would bring deep budget expertise to the table as a former White House budget director under President George W. Bush. He could help Romney win Ohio, which Obama won in 2008 on his way to victory over Republican Senator John McCain.

Martinez could help with Hispanics and women voters who thus far have been unexcited about Romney. And the bludgeoning style of Christie would help energize Republican voters.

Republican strategists say ramping up conservative enthusiasm for turning out to vote with the more moderate Romney at the head of the ticket is a key winning the uphill fight against Obama.

"Ultimately Romney will need to attract independents to win. But he has to start by consolidating conservatives and the best and easiest way to do that is with a VP pick that shores up the base and creates some enthusiasm," said Republican strategist Mark McKinnon.

Word is that Romney has yet to begin his search in earnest, a point he stressed on Thursday in an interview with Fox News Radio's "Kilmeade and Friends."

"I've got no predictions on who No. 2 will be," said Romney. "I've still got to make sure that I'm No. 1."

Republican experts caution against using the selection to satisfy one part or another of the Republican Party.

"The most important thing is to pick somebody who can be president," said Republican strategist Mike DuHaime, who has advised Christie in the past. "In many ways this is the most presidential decision that a candidate makes."

Some potential running mates have publicly declared they do not want the job, like Rubio, and others have been cool to the idea, such as Christie.

"I'm not going to be the vice president," Rubio said in Florida this week.

Also ruling out the idea were Martinez and South Carolina Governor Nikki Haley, although vice presidential candidates have a habit of denying they are interested in the job, right up until they accept it.

Some potential vice presidential running mates this year might want to hold their fire until they can run for the Republican presidential nomination in 2016 should Romney fail to defeat Obama.

"There are plenty of Republicans who would make a great vice presidential candidate, however, some may feel better prepared running in the next election and rather than being put upon a pedestal prematurely," said Republican strategist Ron Bonjean.